Three-Phase Open-End Induction Motor Drive Interfaced to Higher Voltage DC Bus

In applications that require a three-phase induction motor (IM) to be driven by an inverter from a dc bus input of much higher voltage than needed, the option is to use a step down dc-dc converter before the inverter or use high-voltage rating switches in the inverter along with low modulation index. In either case, disadvantages include poor efficiency, high-voltage rated switches, etc. In open-end winding three-phase IM drives, the three separated windings are driven by three-phase inverters from both sides. The arrangement is equivalent to three one-phase inverters driving each winding separately from the same dc bus in parallel. This article proposes an inverter scheme for open-end IM drives, using a one-phase inverter for each winding supply, but all three inverters being connected in series by their dc bus to the higher applied dc voltage. Unlike existing techniques for interfacing an IM drive to a higher voltage dc bus, the proposed scheme requires lower voltage switches with lower voltage bus capacitors to drive the lower voltage motor from a higher voltage dc bus. The series-connected dc bus capacitor voltages are shown to remain balanced during normal operation.